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Date: Tue, 15 Mar 2022 20:50:56 +0100
From: Markus Wichmann <nullplan@....net>
To: musl@...ts.openwall.com
Subject: Re: Possible PEBKAC or Bug in musl Semaphores and/or Mutexes
On Tue, Mar 15, 2022 at 12:55:38PM -0600, Gavin Howard wrote:
> I am pretty sure that this is the right place and that it is a bug in
> musl.
Once more we find someone blaming the implementation for their own
mistake. From your repository:
| y_Status
| y_strucon_rwlock_wrlock(y_strucon_rwlock* l)
| {
| y_ThreadData d = y_strucon_thread_os_get();
|
| yc_assert(l != NULL, YC_ASSERT_NULL);
| yc_assert(d != NULL, YC_ASSERT_NULL);
|
| y_THREAD_TRYLOCK1(d);
|
| y_Status s = y_strucon_rwlock_os_rdlock(l);
|
| return s;
| }
The mistake is in this function. See what the function is called and
what subfunction it calls? No wonder multiple threads can take the lock
simultaneously.
Also, while reading I found a glaring mistake in y_THREAD_TRYUNLOCK1(),
which I shall leave as homework to the reader.
Ciao,
Markus
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